A flame retardant is a compound, which is added to base materials and can suppress base materials igniting or change burning properties of base materials. Currently, plastics, textiles, and coatings have been widely applied to building materials, interior decorating materials, electronic and electric devices, and communication products. However, these materials having poor igniting resistance usually cause significant loss of lives and wealth. Therefore, it becomes more and more important to utilize flame retardants.
In general, halogen-containing flame retardants are used, especially bromine-containing flame retardants. In order to reach the severe requirement for retarding flame, for example, UL 94V-0 grade, adjuvant agents, such as antimonous oxide, are employed. Since antimonous oxide is a carcinogen compound and such bromine-containing flame retardants release erosive bromide free radicals and hydrogen bromide gas, and toxic bromide volatiles after burning, those materials having bromine-containing flame retardants or antimonous oxide are really harmful to human bodies and environments.
Phosphorus-containing flame retardants are the most common used flame retardants to substitute the aforementioned bromine-containing flame retardants. For example, red phosphorus or other phosphorus-containing organic compounds are used as flame retardants. However, as these flame retardants are directly added to base materials, a high adding amount is needed in order to reach a certain flame retarding effect. Moreover, due to their low molecular weight and high migration, properties of base materials, such as electric properties, will be adversely affected.
Compared with phosphorus-containing flame retardants, amino phosphate flame retardants do not have the above-mentioned shortcomings. Generally, the conventional methods for preparing amino phosphate compounds include wet-type and dry-type methods. With respect to wet-type methods, reactants are fist dissolved in solvents and stirred to become solution or emulsion. Then, the solution or emulsion is heated to perform solvent reaction or emulsion reaction to synthesize a liquid product of a flame retardant. If a powdery product is requested, the liquid product is subjected to exclude solvents as disclosed in U.S. Pat. No. 6,008,349. During drying, several disadvantages are raised: the solvents remained in the flame retardant will produce stink and toxicity; energy and solvents will be consumed due to evaporating solvents by heat, resulting in higher process and product cost; and volatilization of solvents will cause environmental contaminations and healthy injuries, being adverse to production.
With respect to dry-type methods, the reactants are pulverized, mixed, calcined, cooled and granulated at a temperature from 300 to 400° C. to obtain the desired products as depicted in JP-A-H11-130413 and U.S. Pat. No. 3,920,796. However, they have drawbacks that the reactions must undergo high temperature process and the steps of preparations are complicated.
To overcome the above-mentioned problems, the present invention has been achieved after the inventors intensively study and make improvements.